1. Field of the Invention
The present invention relates to a radio monitoring technology for monitoring usage of a radio wave.
2. Description of the Related Art
In recent years, a mobile phone and a personal wireless device, etc. become popular. Short-distance communication such as a wireless LAN system using wireless system has been also spreading. For this reason, frequency allocation for various wireless communications is approaching a limit. On the other hand, a wireless communication is important communication resources used by public organizations and also used for a communication in case of disaster and emergency. Therefore, a technology for monitoring a state of use of a radio wave and technology for identifying a transmission source transmitting an unauthorized radio wave have been needed.
For example, JP-A-1997-211039 discloses a radio station distinction apparatus for distinguishing a radio station. This apparatus includes a down converter, a digital spectrum analyzer and a calculation unit. The down converter converts a received signal into an intermediate frequency signal. The digital spectrum analyzer converts this intermediate frequency signal into digital frequency component data. The calculation unit calculates change pattern information of a center frequency of this digital frequency component data.
This radio station distinction apparatus previously calculates the change pattern information of a center frequency of the digital frequency component data for each known radio station and stores the calculation result in the apparatus.
The calculation unit calculates a degree of similarity between received signal change pattern information and change pattern information of a plurality of known radio stations. Then, the calculation unit recognizes a radio station with the highest degree of similarity as a radio station having transmitted this received signal.
The apparatus disclosed in JP-A-1997-211039 can distinguish a model of a radio station which is a transmission source of a radio wave and a mobile station itself. However, JP-A-1997-211039 does not disclose a mechanism to know a location of the radio station thus distinguished. Accordingly, even if a model of a radio station and a mobile station itself are distinguished, a location of the radio station is unknown. Therefore, a location of a radio station for monitoring cannot be traced. Even if the technology disclosed in JP-A-1997-211039 is used in combination with the transmitting location identification technology, an observer is required to use both the technologies disclosed in JP-A-1997-211039 and the transmitting location identification technology simultaneously for monitoring. Generally, it is not guaranteed that a mobile station A identified by the technology disclosed in JP-A-1997-211039 and a mobile station B existing at a location identified by using the transmitting location identification technology are identical. Accordingly, an observer needs to continue monitoring, while confirming that the mobile station A and the mobile station B are identical. Therefore, observer's burden increases. It also means that when an observer is absent, monitoring can not be performed.